1. Field of the Invention
The present invention relates to a disk drive apparatus for a high density DVD etc., more particularly relates to a centering mechanism fit into a center through hole of a disk to center and hold the disk.
2. Description of the Related Art
The disk drive apparatus disclosed in Japanese Patent Publication (A) No. 2007-59040 (FIG. 2) has a rotary table fit on a motor shaft and carrying a disk, and has a centering part elastically biased in an axial direction away from the insides of a center hole of this rotary table and fit into a center through hole of the disk to center and hold the disk. The centering part has elastic abutting parts abutting against the inner circumferential edge of the center through hole and has a surface roughness Ry of the abutting surfaces of the elastic abutting parts in the range of about 5 μm≦Ry≦about 20 μm.
The reason why the abutting surfaces are given such a surface roughness Ry is that a jamming phenomenon where the elastic abutting parts are pushed unilaterally by the centrifugal force directed in one direction due to imbalance of the disk occurring during high speed rotation, the abutting force of the disk and elastic abutting parts becomes stronger, and the disk and the elastic abutting parts end up jamming can be prevented by the lower frictional coefficient when the elastic abutting parts move in the axial direction and therefore recording and reproduction error can be eliminated.
The surface roughness Ry is obtained by setting the surface roughness of the mold used when forming the centering part from plastic, but due to the environment of use of the disk drive apparatus and the years of use, dirt and oil will deposit on the abutting surfaces and wear will occur. The frictional coefficient of the abutting surfaces does not depend only the surface roughness Ry, so the reliability of prevention of the jamming phenomenon is low.
Further, as a practical problem, at the time of molding the plastic, the precision of molding thickness is usually 0.1 mm (100 μm) or so, therefore trying to obtain the above level of surface roughness in products would lead to a drop in yield.